The present invention relates to a semiconductor memory device which needs a refresh operation, and principally to a technology effective for application to a pseudo static RAM or the like which executes an external read/write operation and a refresh operation executed by an internal circuit during one memory cycle to conceal the refresh operation from outside, thereby being usable equivalently to a static RAM (Random Access Memory) on an equivalent basis.
In order to make it possible to handle a DRAM in a manner similar to an SRAM (Static Random Access Memory), a so-called time multiplex type DRAM wherein a read/write operation and a refresh operation are executed during one cycle with their times being assigned thereto, or the two operations are executed only when the read/write operation and the refresh operation compete with each other, has been proposed in Unexamined Patent Publication No. Sho 61(1985)-71494 (Related Art 1). Further, a pseudo SRAM wherein address transition detectors for a row and a column are respectively provided and a static column operation is controlled based on these detected signals, has been proposed in Unexamined Patent Publication No. Hei 1(1989)-94593 (Related Art 2).
In the related art 1, no page read mode is disclosed. The related art 1 does not show architecture for performing switching to a high-speed sequential read mode when only a column address has changed. The related art 2 has a problem in that it corresponds to a page read mode but pays no consideration to the refresh operation, and when page read is done continuously, a word line remains activated and hence refresh cannot be performed, whereby the page read is restricted by the refresh operation.
An object of the present invention is to provide a semiconductor memory device which is made identical in usability to a static RAM by using dynamic memory cells and realizes a high-speed memory cycle time. The above, other objects and novel features of the present invention will become apparent from the description of the present specification and the accompanying drawings.
A summary of a typical one of the inventions disclosed in the present application will be described in brief as follows: A pseudo static RAM having a time multiplex mode which, when instructions for a memory operation for reading memory information from each of memory cells each requiring a refresh operation for periodically holding the memory information, or writing the same therein is issued, carries out an addressing-based autonomous refresh operation different from the memory operation before or after the memory operation, includes address signal transition detectors for a row and a column, and a page mode which independently performs a column address selecting operation according to an address signal transition detect signal of the column address signal transition detector.